Method of treating a carbon current collection brush and brush resulting therefrom

ABSTRACT

A method of treating a carbon current collection brush for increased high temperature life which comprises contacting at least one surface of the brush with a solution of phosphorus oxychloride and baking the brush at a temperature from 200*C to 700*C thereby reducing the amount of phosphorus oxychloride to 1 to 4 weight percent of the brush weight. A modified method includes the above method steps but includes a pretreatment step in a mild aqueous oxidant, such as, a hypochlorite solution. A carbon current collection brush has a carbon body and the body contains from about 0.1 to 5 weight percent of phosphorus oxychloride.

[ 5] Nov. 13, 1973 I [75] inventor:

[ METHOD OF TREATING A CARBON CURRENT COLLECTION BRUSH AND BRUSH RESULTING THEREFROM Douglas W. McKee, Burnt Hills, NY.

[73] Assignee: General Electric Company,

Schenectady, NY.

221 Filed: Jan. 10, 1972 21 Appl. No.: 216,417

2,739,254 3/1956 Moberly 117/228 2,715,080 8/1955 Cashell.. 117/213 3,342,627 9/1967 Paxton 117/228 Primary Examiner-Alfred L. Leavitt Assistant Examiner-MI F. Esposito Attorney-John F. Ahern et al.

[57] ABSTRACT A method of treating a carbon current collection brush for increased high temperature life which comprises contacting at least one surface of the brush with a solution of phosphorus oxychloride and baking the brush at a temperature from 200C to 700C thereby reducing the amount of phosphorus oxychloride to l to 4 weight percent of the brush weight. A modified method includes the above method steps but includes a pretreatment step in a mild aqueous oxidant, such as, a hypochlorite solution. A carbon current collection brush has a carbon body and the body contains from about 0.1 to 5 weight percent of phosphorus oxychloride.

6 Claims, 1 Drawing Figure METHOD OFTREATING A CARBON CURRENT COLLECTION BRUSH AND BRUSH RESULTING THEREFROM This invention relates to methods of treating carbon current collection brushes, and to brushes resulting therefrom and, more particularly, to such methods to produce brushes for operation at brush elevated temperatures.

Carbon current collection brushes are employed in rotating brush-type machines which brushes are generally fabricated of carbon, a relatively poor electrical conductor, reinforced by other materials and graphitized. Graphite is also employed for such brushes. For example, carbon is mixed with a pitch binder and the mixture is graphitized. These brushes are referred therein as carbon current collection brushes or merely as carbon brushes. Such carbon brushes are retained in position by brush holders which generally are in the form of square or rectangular sleeves serving as a guide for any radial motion of the brush resulting from vibration or eccentricity of the armature. The brush holder may be mounted on a bracket to maintain a rigid position spaced from the commutator surface. An adjustable spring connected to the bracket bears on the top surface of the brush to maintain a desired contact pressure of the bottom surface of the brush upon the commutator segments or slip ring.

With such carbon current collection brushes or carbon brushes, as these brushes are generally referred to, the wear rate in electric motors, for example, increases very rapidly with increasing ambient temperature. The life of a typical carbon brush decreases from about 10,000 hours for 0.25 inch wear at 100C to about 500 hours for 0.25 inch wear at 200C. An important contributing factor to increased wear at elevated temperatures is direct oxidation of the carbon brush surface at the sliding interface, leading to loss of carbon as gaseous oxides. This oxidation is catalyzed by the presence of the copper in the commutator or slip ring. Minute particles of copper oxide migrate along the basal planes of the graphite cyrsallites into the interior of the brush producing a catalytic effect which leads to enhanced gasification rates and to increased brush porosity. Various approaches have been employed in attempts to overcome such rapid brush wear including use of lubricants.

' The present invention is directed to an improved method of treating a conventional carbon current collection brush and to an improved carbon brush resulting therefrom which is useful at elevated temperatures.

The primary objects of my invention are to provide a method of treating a carbon brush which brush exhibits characteristics of operability at elevated temperatures and reduced wear rate.

The above objects and other objects, features and advantages of the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

The single FIGURE is a side elevational view, partly in section, of'a carbon brush, made in accordance with my invention, in a brush holder assembly.

In the single FIGURE of the drawing there is shown a brush holder assembly including an improved carbon current collection brush 11 made in accordance with my invention. Carbon brush 11 comprises a body portion 12 and a lower surface portion 13, which surface is in contact with or rides on the surface of a commutator 14 or a slip ring due to the force ofa spring applied by brush spring 15 against the top of body portion 12 of carbon brush 11. Carbon brush 11 is maintained in its desired position relative to cummutator 14 or to a slip ring by means of brush holder 16 which is held in a fixed position spaced from the surface of commutator 14 by means of bracket 17. Brush holder 16 is shown of conventional design comprising a rectangular sleeve fabricated of a high strength metal and serves as a guide for any radial motion of carbon brush 11 resulting from vibration or eccentricity of the armature or commutator. For purposes of simplicity, the flexible copper cable generally described as a brush shunt or pigtail which is. often employed for directing the current from the carbon brush to the brush holder is not illustrated but can be employed, as desired. Carbon brush 11 or at least its surface 13 contains from 0.1 to 5.0 weight of phosphorus oxychloride.

I found that a carbon current collection or carbon brush which contained from 0.1 to 5 weight percent of phosphorus oxychloride therein or at least in a surface portion had an increased operating factor of about 4 versus a conventional carbon collection or carbon brush at amperes/square inch at an elevated temperature of 200C. I found that such operating factor at 200C was further increased to 8 when the brush was pretreated in a sodium hypochlorite solution. Further, the ignition temperature of the carbon brush increased from 770C for an untreated brush to 828C and 880C, respectively, for the above treated brushes.

I found that my method of treating a carbon current collection brush with phosphorus oxychloride inhibited the catalytic effect of the copper oxide which had migrated into the brush from the commutator or slip ring during brush operation. This treatment reduced the normally resulting enhanced gasification rates and increased brush porosity. My improved carbon brush exhibited substantially longer life at elevated temperatures.

I found that I could form an improved carbon current collection brush by treating a conventional carbon brush in the following unique manner. A conventional carbon brush is contacted with phosphorus oxychloride, a volatile liquid which boils at 107C, by immersing the brush therein at room temperature for a period of at least 15 minutes, which time period is suitable to impregnate the brush. After impregnation, the brush is baked out at a temperature of from 200C to 700C for a period of at least 1 hour to remove all but 0.1 to 5.0 weight percent of phosphorus oxychloride. Within this temperature range, I prefer a range of 400 to 700C. I found further that such a baking step is necessary to produce the improved brush of my invention. Higher concentrations of phosphorus oxychloride, which result from no baking or insufficient baking results in a brush with subsequent high friction at the brush commutator or slip ring interface.

I found that the above method can be modified to result in a further improved brush. The modified method includes a pretreatment step of contacting the initial conventional carbon brush with a mild aqueous oxidant solution, such as sodium hypochlorite, which is preferred. In addition to sodium hypochlorite, NaOCl, other suitable mild aqueous oxidant solutions include 0.5 N K Cr O,/H S0,, 0.5 N Na,S,O /I-I,S0 0.5 N KBrO /I-ICl, etc. Of various solution concentrations and times of pretreatment for the sodium hypochlorite, I prefer a percent solution and an immersion time of 2 hours.

Carbon current collection brushes made in accordance with the method of my invention are set forth below:

EXAMPLE 1 A conventional carbon current collection brush of graphitized carbon was contacted with a phosphorus oxychloride solution by being immersed therein for a period of 60 minutes. The brush was then baked at 400C for a period of 1 hour whereby the brush contained 4 weight percent of phosphorus oxychloride.

EXAMPLE 2 Two standard wear tests under load were performed on the brush of Example 1. The first wear test was performed at 110C while the second wear test was performed at an elevated temperature of 200C. Each test involved a standard current rating of 100 amperes per square inch. The brush was mounted in a brush holder' and employed in the fashion shown generally in the single FIGURE of the drawing. In this example and subsequent examples, the standard wear test is to determine the number of hours of brush life until 0.25 inch of the brush surface is worn away. Thus, the results of each test are set forth in hours which is the life of the particular brush. At 110C the brush exhibited 5,500 hours. At 200C the brush exhibited 1,950 hours.

EXAMPLE 3 For comparison purposes with my improved brush of Examples 1 and 2, a conventional carbon current collection brush of graphitized carbon which was not treated in accordance with my method exhibited 10,000 hours of brush life at 1 10C. However, at 200C this conventional carbon brush exhibited only 500 hours of life. Thus, it will be seen that at an elevated temperature of 200C that the carbon brush treated in accordance with my method exhibits almost a four-fold improvement over a conventional carbon brush.

EXAMPLE 4 Another carbon brush was prepared in accordance with my method as set forth above in Example 1. For comparison purposes, an untreated conventional carbon current collection brush of graphitized carbon was also used. Both of these brushes were oxidized in air to determine the ignition temperature. The untreated carbon brush had an ignition temperature of 770 while the carbon brush treated in accordance with my invention had an ignition temperature of 828C.

EXAMPLE 5 EXAMPLE 6 Two standard wear tests under load were performed on the brush of Example 5 in accordance with the procedure set forth in Example 2 above. The brush when subjected to a temperature of 110C showed a brush life of 4,000 hours. The brush when subjected to a temperature of 200C showed a brush life of an identical 4,000 hours. This latter brush life was an eight-fold improvement over an untreated brush.

EXAMPLE 7 Another carbon brush was treated in accordance with my invention as set forth above in Example 57 A conventional current collection brush of graphitizing carbon was also used for comparison purposes. Each carbon brush was then oxidized in air with a resulting ignition temperature of the untreated brush at 770C. The ignition temperature of the carbon brush treated in accordance with my invention as set forth in Example 5 was 880C.

EXAMPLE 8 Three additional carbon brushes were made in accordance with my invention as set forth above in Example 5. However, the time of pretreatment was varied with each of the three brushes. The first carbon brush was pretreated for 30 minutes while the second carbon brush was pretreated for two hours. The third carbon brush was treated for hours-Subsequently, these three carbon brushes were air oxidiiTto determine their ignition temperatures. The first carbon brush, which was pretreated for 30 minuteshad an ignition temperature of 832C. The second carbon brush had an ignition temperature of 880C while the third carbon brush had an ignition temperature of 900C. Thus, it will be noted that the second carbon brush, which had been treated for two hours, resulted in as high an ignition temperature as the carbon brush pretreated for 24 hours and almost as high as ignition temperature as 100 hour treatment for the carbon brush.

While other modifications of the invention and variations thereof which may be employed within the scope of the invention have not been described, the invention is intended to include such as may be embraced within the following claims:

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A method of treating a carbon current collection brush which comprises providing a carbon current collection brush, contacting the brush with a solution of phosphorus oxychloride and baking the brush at a temperature in the temperature range of from 200 to 700C thereby reducing the amount of phosphorus oxychloride in the brush to 1 to 4 weight percent of the brush weight.

2. A method of treating a carbon current collection brush as in claim 1, in which the brush is baked at a temperature in the temperature range of from 400 to 700C for at least one hour.

3. A method of treating a carbon current collection brush as in claim 1, in which the brush is pretreated in a mild aqueous oxidant solution.

4. A method of treating a carbon current collection brush as in claim 3, in which the oxidant solution is sodium hypochlorite.

5. A method of treating a carbon current collection brush as in claim 3, in which the brush is pretreated in a 5 percent solution of sodium hypochlorite for a period of two hours.

6. A method of treating a carbon current collection brush as in claim 1, in which the brush is pretreated in a 5 percent solution of sodium hypochlorite for a period of two hours, and the brush is baked at a temperature of 400C for one hour.

* I I I l 

2. A method of treating a carbon current collection brush as in claim 1, in which the brush is baked at a temperature in the temperature range of from 400* to 700*C for at least one hour.
 3. A method of treating a carbon current collection brush as in claim 1, in which the brush is pretreated in a mild aqueous oxidant solution.
 4. A method of treating a carbon current collection brush as in claim 3, in which the oxidant solution is sodium hypochlorite.
 5. A method of treating a carbon current collection brush as in claim 3, in which the brush is pretreated in a 5 percent solution of sodium hypochlorite for a period of two hours.
 6. A method of treating a carbon current collection brush as in claim 1, in which the brush is pretreated in a 5 percent solution of sodium hypochlorite for a period of two hours, and the brush is baked at a temperature of 400*C for one hour. 